Amyloidosis is a serious and usually fatal disease caused by accumulation in the tissues of abnormal insoluble protein fibres known as amyloid fibrils1. These are derived from different proteins in different forms of the disease but all amyloid fibrils share a common cross-β core structure and all are derived by misfolding of normally soluble precursor proteins. In addition to the amyloid fibrils themselves, amyloid deposits are always rich in proteoglycans, some of which are tightly bound to the fibrils2. A normal non-fibrillar plasma protein, serum amyloid P component (SAP), is also always present in amyloid deposits by virtue of its avid specific calcium dependent binding to all types of amyloid fibrils3,4.
Human SAP is a constitutive protein in the plasma5, at a concentration of around 20-40 mg/l and with a total of about 50-100 mg of SAP in the combined plasma and extravascular compartments both of normal individuals and patients with diseases other than amyloidosis6. In contrast, in patients with amyloid, SAP is also specifically concentrated in the amyloid deposits and in an individual with extensive systemic amyloidosis there may be as much as 20,000 mg of SAP in the amyloid7.
Amyloid deposits are extracellular and they cause disease by progressive accumulation until they damage the structure and thus the function of whatever tissue they occupy1. There is very rarely any inflammatory or ‘foreign body’ response to amyloid deposition, either seen locally in the tissues or suggested by systemic markers of inflammation. In so called systemic amyloidosis the deposits can be present in any tissue or organ in the body but deposits are never seen within the brain substance in these forms of the disease. Systemic amyloidosis is the cause of about 1 per 1000 of all deaths in developed countries, and is always fatal unless the abundance of the protein which is the precursor of the amyloid fibrils can be sufficiently and persistently reduced. This is difficult to achieve in many forms of amyloidosis and may be impossible, and there is thus a major unmet medical need1,8. Local forms of amyloidosis, in which the deposits are confined to a single anatomical site or a single tissue or organ system also occur and may cause serious disease1,8.
In amyloidosis the damage to the structure and function of tissues and organs which leads to clinical disease is unequivocally caused by the progressive accumulation of the amyloid deposits themselves. However there are other conditions in which amyloid deposits are always present, most importantly Alzheimer's disease and type 2 diabetes mellitus, in which the contribution of the amyloid deposition to the pathogenesis of disease, specifically loss of cognitive and pancreatic islet function respectively, is not known1. However, amyloid deposits anywhere else in the body are demonstrably pathogenic and it is likely that the cerebral amyloid deposits of Alzheimer's disease and the islet amyloid deposits of type 2 diabetes are also harmful. Since treatment which clears amyloid deposits in systemic and local amyloidosis will certainly be therapeutic1, removal of the amyloid deposits in Alzheimer's disease and type 2 diabetes should also be clinically beneficial.
Systemic amyloid A protein (AA) amyloidosis is readily induced in mice by chronic inflammation following intravenous injection of an extract of amyloidotic tissue containing amyloid fibrils, and known as amyloid enhancing factor9. This model very closely resembles human AA amyloidosis with major amyloid deposition in the spleen and liver10. With the relatively brief period of amyloid induction, for example as used in the experiments described herein, there is very little amyloid deposition elsewhere. The AA protein which forms the amyloid fibrils is derived from its circulating precursor, serum amyloid A protein (SAA), which is an acute phase protein. The plasma concentration of SAA rises sharply from its normal trace value of less than 5 mg/l in response to almost any form of inflammation and tissue damage and can persist at values up to 1000 mg/l, or even more, in the face of persistent stimulation. This increased production of SAA is a necessary precondition for development of AA amyloidosis, and both in humans and in mice, when the SAA concentration falls to normal, amyloid deposition stops and existing amyloid deposits can regress10-12. In the absence of continued SAA production, spontaneous regression of AA amyloid deposits is universal in the mouse model11 but proceeds at a variable rate which must be appropriately accommodated in the design of therapeutic experiments.
European patent application EP 0 915 088 discloses compounds which are competitive inhibitors of binding of SAP to amyloid fibrils, as well as methods for their manufacture. A preferred compound disclosed in EP 0 915 088 is (R)-1-[6-[(R)-2-Carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC), however, any of the compounds described therein, or any other compound which depletes circulating SAP can be used in the practice of the present invention. International Patent Application WO 2004/099173, incorporated herein by reference, also describes palindromic compounds that could also be used in the practice of the present invention.
In human SAP transgenic mice, human SAP is present in both the circulation and the amyloid deposits. The drug (R)-1-[6-[(R)-2-Carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC) is specifically bound by human SAP in a complex composed of two native pentameric SAP molecules and 5 CPHPC molecules16. This complex is recognised as abnormal by the liver and is very rapidly taken up by the hepatocytes and degraded, thus efficiently clearing SAP from the circulation16. Plasma SAP concentrations remain very low for as long as the drug is administered16. CPHPC is extremely well tolerated and neither the drug itself nor the SAP depletion it produces have caused any adverse effects16. There is evidence of clinical benefit from CPHPC treatment in human systemic amyloidosis patients, especially with respect to preservation of renal function in individuals with predominantly renal amyloidosis.
However, despite these promising observations with CPHPC, swift and optimal therapeutic efficacy capable of preserving organ function and prolonging life in patients with systemic amyloidosis will require substantial or complete clearance of the amyloid deposits.
International patent application WO04/059318 describes methods which are asserted to enhance fibrocyte formation which comprise the provision of compositions which bind SAP. Such compositions include anti-SAP antibodies and CPHPC. However, WO04/059318 does not describe the treatment of diseases associated with amyloid deposition. Moreover, WO04/059318 does not describe the specific combination of an anti-SAP antibody and CPHPC. Furthermore, recent data indicate that SAP is not associated with fibrocyte inhibition, and thus that SAP depletion does not enhance fibrocyte production20.
Accordingly, there is a need in the art for improved therapeutic efficacy in patients with systemic amyloidosis to preserve organ function and prolong life.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.